Skin cancer is a disease in which malignant (cancer) cells form
in the tissues of the skin.

The skin is the body's largest organ. It protects against heat,
sunlight, injury, and infection. Skin also helps control body temperature and stores water, fat, and vitamin D. The skin has several layers, but the two main layers are the epidermis (top or outer layer) and the dermis (lower or inner layer). Skin cancer begins in the epidermis, which is made up of three kinds of cells:

Melanocytes: Found
in the lower part of the epidermis, these cells make melanin, the pigment
that gives skin its natural color. When skin is exposed to the sun, melanocytes
make more pigment and cause the skin to tan, or darken. Cancer that forms in melanocytes is called melanoma.

Anatomy of the skin, showing the epidermis, dermis, and subcutaneous tissue.

Nonmelanoma skin cancer is the most common cancer in the United
States.

Basal cell carcinoma and squamous cell carcinoma are also called nonmelanoma skin cancer and are the most common forms of skin cancer. Most basal cell and squamous cell
skin cancers can be cured.

Melanoma is more likely to spread to nearby tissues and other parts of the body and can be harder to cure. Melanoma is easier to cure if the tumor is found before it spreads to the dermis (inner layer of skin). Melanoma is less likely to cause death when it is found and treated early.

Anatomy of the skin, showing the epidermis, dermis, and subcutaneous tissue. Melanocytes are in the layer of basal cells at the deepest part of the epidermis.

In the United States, the number of cases of nonmelanoma skin cancer seems to have increased in recent years. The number of cases of melanoma has increased over the last 30 years. Part of the reason for these increases may be that people are more aware of skin cancer. They are more likely to have skin exams and biopsies and to be diagnosed with skin cancer.

Over the past 20 years, the number of deaths from melanoma has decreased slightly among white men and women younger than 50 years. During that time, the number of deaths from melanoma has increased slightly among white men older than 50 years and stayed about the same among white women older than 50 years.

See the following PDQ summaries for more information about skin cancer:

Being exposed to ultraviolet radiation may increase
the risk of skin cancer.

Anything that increases your chance of getting a disease
is called a risk factor. Having a risk factor does not mean that you will get cancer; not having risk factors doesn't mean that you will not get cancer. People who think they may be at risk should discuss this with their doctor.

Being exposed to ultraviolet (UV)
radiation and having skin that is sensitive to UV radiation are risk factors for skin cancer. UV radiation is the name for the invisible rays
that are part of the energy that comes from the sun. Sunlamps and tanning
beds also give off UV radiation.

Risk factors for
nonmelanoma and melanoma cancers are not the same.

Nonmelanoma skin cancer risk factors include:

Being exposed to natural sunlight or artificial sunlight (such as from tanning beds) over long periods of time.

Having a fair complexion, which includes the following:

Fair skin that freckles and burns easily, does not tan, or tans poorly.